Systems and methods for selecting light emitters for emitting light

ABSTRACT

An example circuit includes a plurality of light emitters connected in parallel between a first node and a second node. The circuit also includes a plurality of capacitors, with each capacitor corresponding to one of the light emitters, and a plurality of discharge-control switches, with each discharge-control switches corresponding to one of the capacitors. The circuit further includes a pulse-control switch connected to the plurality of light emitters. During a first period, the pulse-control switch restricts current flow, and each of the plurality of capacitors is charged via the first node. During a second period, one or more of the plurality of discharge-control switches allows current flow that discharges one or more corresponding capacitors. During a third period, the pulse-control switch allows current flow that discharges one or more undischarged capacitors of the plurality of capacitors through one or more corresponding light emitters.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

A Light Detection and Ranging (LIDAR) device is used for sensing aspectsof an environment. A plurality of light emitters emit light to anenvironment surrounding the device, and a plurality of light detectorsdetect reflected light. Based on time differences between lightemissions and receiving the reflected light, the LIDAR device cangenerate three-dimensional (3D) point cloud data that can be interpretedto render a representation of the environment.

Conditions might exist where it is desirable to sense some portions ofthe environment but not others. For example, reflections from someobjects in the environment (e.g., retroreflectors) might interfere withsensing neighboring portions of the environment.

SUMMARY

In a first example, a circuit is provided. The circuit includes aplurality of light emitters connected in parallel between a first nodeand a second node. The circuit includes a plurality of capacitors,wherein each capacitor in the plurality of capacitors corresponds to arespective light emitter in the plurality of light emitters. The circuitincludes a plurality of discharge-control switches, wherein eachdischarge-control switch corresponds to a respective capacitor in theplurality of capacitors. The circuit includes a pulse-control switchconnected to the plurality of light emitters. During a first period, thepulse-control switch restricts current flow and each capacitor in theplurality of capacitors is charged via the first node. During a secondperiod, one or more of the plurality of discharge-control switchesallows current flow that discharges one or more corresponding capacitorsof the plurality of capacitors. During a third period, the pulse-controlswitch allows current flow that discharges one or more undischargedcapacitors of the plurality of capacitors through one or morecorresponding light emitters of the plurality of light emitters, therebycausing the one or more corresponding light emitters to emit respectivepulses of light.

In a second example, a method is provided. The method includes, during afirst period, (i) using a pulse-control switch to restrict current flowthrough a plurality of light emitters, and (ii) charging a plurality ofcapacitors via a first node. The method includes, during a secondperiod, using one or more discharge-control switches to allow currentflow that discharges one or more corresponding capacitors of theplurality of capacitors. The method includes, during a third period,using the pulse-control switch to allow current flow and therebydischarge one or more undischarged capacitors of the plurality ofcapacitors through one or more corresponding light emitters of theplurality of light emitters, thereby causing the one or morecorresponding light emitters to emit respective pulses of light.

In a third example, a non-transitory computer readable medium isprovided. The non-transitory computer readable medium has instructionsstored thereon that when executed by a processor cause performance of aset of functions. The set of functions includes, during a first period,(i) using a pulse-control switch to restrict current flow through aplurality of light emitters, and (ii) charging a plurality of capacitorsvia a first node. The set of functions includes, during a second period,using one or more discharge-control switches to allow current flow thatdischarges one or more corresponding capacitors of the plurality ofcapacitors. The set of functions includes, during a third period, usingthe pulse-control switch to allow current flow and thereby discharge oneor more undischarged capacitors of the plurality of capacitors throughone or more corresponding light emitters of the plurality of lightemitters, thereby causing the one or more corresponding light emittersto emit respective pulses of light.

In a fourth example, a method for scanning an environment of anautonomous vehicle is provided. The method may include determiningportions of the environment that may include retroreflectors. The methodmay further include selectively disabling capabilities of a LIDAR toscan those portions. The method may further include scanning otherportions of the of the environment with the LIDAR. Selectively disablingcapabilities of the LIDAR to scan those portions may include selectivelypreventing the LIDAR from transmitting light to those portions of theenvironment that may include retroreflectors. Selectively preventing theLIDAR from transmitting light to those portions of the environment thatmay include retroreflectors may include selectively preventing one ormore transmitters (e.g., light emitters, such as laser diodes) fromemitting light at a certain time.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescription provided in this summary section and elsewhere in thisdocument is intended to illustrate the claimed subject matter by way ofexample and not by way of limitation.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a block diagram of a system including a LIDAR device,according to an example embodiment.

FIG. 1B is a block diagram of a LIDAR device, according to an exampleembodiment.

FIG. 2 illustrates an environment of a LIDAR device, according to anexample embodiment.

FIG. 3A illustrates a pulser circuit of a LIDAR device at a first time,according to an example embodiment.

FIG. 3B illustrates a pulser circuit of a LIDAR device at a second time,according to an example embodiment.

FIG. 3C illustrates a pulser circuit of a LIDAR device at a third time,according to an example embodiment.

FIG. 3D illustrates a pulser circuit of a LIDAR device at a fourth time,according to an example embodiment.

FIG. 4 is a block diagram of a method, according to an exampleembodiment.

DETAILED DESCRIPTION

Example methods, devices, and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as being an “example” or “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or features. Other embodiments can be utilized, and otherchanges can be made, without departing from the scope of the subjectmatter presented herein.

Thus, the example embodiments described herein are not meant to belimiting. Aspects of the present disclosure, as generally describedherein, and illustrated in the figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall embodiments, with the understanding that not allillustrated features are necessary for each embodiment.

By the term “about” or “substantially” with reference to amounts ormeasurement values described herein, it is meant that the recitedcharacteristic, parameter, or value need not be achieved exactly, butthat deviations or variations, including for example, tolerances,measurement error, measurement accuracy limitations and other factorsknown to those of skill in the art, may occur in amounts that do notpreclude the effect the characteristic was intended to provide.

I. Overview

A LIDAR device can include one or a plurality of light emitters that canemit pulses of light. For example, the light emitter may be a laserdiode. A selector circuit can be used to select which of the lightemitters are used to emit light and which are not. For example, it maybe desirable that one or more of the light emitters are not used to emitlight in order to avoid illuminating retroreflectors or otherhighly-reflective surfaces. Such surfaces may flood light detectors onthe LIDAR device with reflected portions of light emitted from the lightemitters and thus impede aspects of representing the received reflectedportions of light and interpreting resulting data. For example, this mayintroduce ambiguity in determining 3D point cloud data or may biasdata-processing operations that use the 3D point cloud data, such asedge-detection or object detection operations.

In an example embodiment, the pulser circuit includes a plurality oflaser diodes that are connected in parallel. For example, the laserdiodes could all have a common cathode (e.g., a device may include eightlaser diode bars with a common cathode), or the cathodes of the laserdiodes could be connected together at a cathode node. The common cathodeor cathode node is connected to the drain of a pulse-control switch(e.g., a transistor, such as a GaNFET or other type of field-effecttransistor, a bipolar transistor, a control switch, a limit switch, oranother type of switching device configured to alternatively allow orstop current flow in a circuit). For example, the pulse-control switchmay be a pulse-control transistor. In such examples, the source of thepulse-control transistor is connected to ground. The gate of thepulse-control transistor is connected to a driver circuit. The anode ofeach laser diode is connected to the cathode of a respective chargingdiode, a respective capacitor, and a respective discharge-controlswitch. The pulser circuit further includes an inductor. One end of theinductor is connected to an adjustable voltage source. The other end ofthe inductor is connected to the anodes of the charging diodes.

The pulser circuit can be operated in accordance with a repeating pulseperiod, each pulse period corresponding to emissions of light from thelight emitters. Each pulse period, in turn, can include a first period(i.e., a charging period), a second period (i.e., a selective dischargeperiod), and a third period (i.e., a pulse emission period). During thecharging period, the pulse-control switch is off, all of thedischarge-control switches are off, and the voltage source is turned on.The voltage source causes a current to flow through the inductor, whichcharges each of the capacitors through their associated charging diodes.During the selective discharge period, one or more of thedischarge-control switches are turned on, thereby discharging theassociated capacitors. During the pulse emission period, thepulse-control switch is turned on, which causes the capacitors that havenot already been discharged to discharge through their associated laserdiodes and the pulse-control switch. As a result, a discharge currentflows through each laser diode that has not had its associated capacitordischarged during the selective discharge period, thereby causing eachsuch laser diode to emit a pulse of light.

In some examples, a shift register is used to control thedischarge-control switches. For example, the discharge-control switchescan be transistors or other switching devices. Accordingly, as referredto herein, the term functionality described with respect to a“discharge-control transistor” can also be achieved using other types ofswitching devices, such as switches. In this approach, the shiftregister is loaded with data (e.g., N bits of data for N laser diodes,or N bits of data for 2{circumflex over ( )}N switches, depending on theencoding of the shift register), with each bit of data determiningwhether the discharge-control switch for a particular laser diode is tobe turned on during the selective discharge period or remain off. Forexample, a “1” may indicate that a discharge-control switch is to beturned on and a “0” may indicate that a discharge-control switch is toremain off, or vice versa. The outputs of the shift register areconnected to the gates of the discharge-control switches, and therebyselect which capacitors to discharge during the selective dischargeperiod, and by proxy, select which capacitors that remain charged andare capable of discharging during the pulse emission period.

In some examples, the adjustable voltage source can be controlled toapply different voltages to the inductor. For example, in a default modeof operation, the adjustable voltage source may be controlled to apply avoltage V1 to the inductor, which causes each of the capacitors tocharge up to a voltage of Vcap1 (e.g., Vcap1 could be about 2×V1). Whenthe capacitors discharge through their respective laser diodes, theemitted light pulses may have a first peak power level. However, forshort periods of time (e.g., based on thermal constraints), theadjustable voltage source may be controlled to apply a voltage V2 to theinductor in which V2>V1. This causes the capacitors to charge up to ahigher voltage, Vcap2 (e.g., Vcap2 could be about 2×V2). And, when thecapacitors discharge through their respective laser diodes, the emittedlight pulses may have a second, higher peak power level. Controlling thevoltage levels of the capacitors may alternatively or additionallyinvolve applying a voltage for a period of time associated with chargingthe capacitor (i.e., a “charging period”). For example, a desired powerlevel of a light pulse can be determined that is associated with acharge level of the capacitors. The capacitors may be charged for aperiod of time (e.g., based on a known capacitance of the capacitors andthe applied voltage) associated with the power level. In this manner, apower level of each light pulse can be precisely controlled by settingthe charging period for the capacitors. Additionally or alternatively,each charged capacitor can be discharged by a predetermined amount priorto the emission period to achieve a desired voltage level and therebycontrol a power level of each light pulse.

II. Example Systems

FIG. 1A is a block diagram of a system including a LIDAR device,according to an example embodiment. In particular, FIG. 1A shows asystem 100 that includes a system controller 102, a LIDAR device 110, aplurality of sensors 112, and a plurality of controllable components114. System controller 102 includes processor(s) 104, a memory 106, andinstructions 108 stored on the memory 106 and executable by theprocessor(s) 104 to perform functions.

The processor(s) 104 can include on or more processors, such as one ormore general-purpose microprocessors and/or one or more special purposemicroprocessors. The one or more processors may include, for instance,an application-specific integrated circuit (ASIC) or afield-programmable gate array (FPGA). Other types of processors,computers, or devices configured to carry out software instructions arecontemplated herein.

The memory 106 may include a computer readable medium, such as anon-transitory computer readable medium, which may include withoutlimitation, read-only memory (ROM), programmable read-only memory(PROM), erasable programmable read-only memory (EPROM), electricallyerasable programmable read-only memory (EEPROM), non-volatilerandom-access memory (e.g., flash memory), a solid state drive (SSD), ahard disk drive (HDD), a Compact Disc (CD), a Digital Video Disk (DVD),a digital tape, read/write (R/W) CDs, R/W DVDs, etc.

The LIDAR device 110, described further below, includes a plurality oflight emitters configured to emit light (e.g., in light pulses) andlight detectors configured to detect light (e.g., reflected portions ofthe light pulses). The LIDAR device 110 may generate 3D point cloud datafrom outputs of the light detectors, and provide the 3D point cloud datato the system controller 102. The system controller 102, in turn, mayperform operations on the 3D point cloud data to determine thecharacteristics of an environment (e.g., relative positions of objectswithin an environment, edge detection, object detection, proximitysensing, or the like).

Similarly, the system controller 102 may use outputs from the pluralityof sensors 112 to determine the characteristics of the system 100 and/orcharacteristics of the environment. For example, the sensors 112 mayinclude one or more of a Global Positioning System (GPS), an InertialMeasurement Unit (IMU), an image capture device (e.g., a camera), alight sensor, a heat sensor, and other sensors indicative of parametersrelevant to the system 100 and/or the environment). The LIDAR device 110is depicted as separate from the sensors 112 for purposes of example,and may be considered a sensor in some examples.

Based on characteristics of the system 100 and/or the environmentdetermined by the system controller 102 based on the outputs from theLIDAR device 110 and the sensors 112, the system controller 102 maycontrol the controllable components 114 to perform one or more actions.For example, the system 100 may correspond to a vehicle, in which casethe controllable components 114 may include a braking system, a turningsystem, and/or an accelerating system of the vehicle, and the systemcontroller 114 may change aspects of these controllable components basedon characteristics determined from the LIDAR device 110 and/or sensors112 (e.g., when the system controller 102 controls the vehicle in anautonomous mode). Within examples, the LIDAR device 110 and the sensors112 are also controllable by the system controller 102.

FIG. 1B is a block diagram of a LIDAR device, according to an exampleembodiment. In particular, FIG. 1B shows a LIDAR device 110, having acontroller 116 configured to control a plurality of light emitters 124and a plurality of light detectors 126. The LIDAR device 110 furtherincludes a pulser circuit 128 configured to select and provide power torespective light emitters of the plurality of light emitters 124 and aselector circuit 130 configured to select respective light detectors ofthe plurality of light detectors 126. The controller 116 includesprocessor(s) 118, a memory 120, and instructions 122 stored on thememory 120.

Similar to processor(s) 104, the processor(s) 118 can include one ormore processors, such as one or more general-purpose microprocessorsand/or one or more special purpose microprocessors. The one or moreprocessors may include, for instance, an application-specific integratedcircuit (ASIC) or a field-programmable gate array (FPGA). Other types ofprocessors, computers, or devices configured to carry out softwareinstructions are contemplated herein.

Similar to memory 106, the memory 120 may include a computer readablemedium, such as a non-transitory computer readable medium, such as, butnot limited to, read-only memory (ROM), programmable read-only memory(PROM), erasable programmable read-only memory (EPROM), electricallyerasable programmable read-only memory (EEPROM), non-volatilerandom-access memory (e.g., flash memory), a solid state drive (SSD), ahard disk drive (HDD), a Compact Disc (CD), a Digital Video Disk (DVD),a digital tape, read/write (R/W) CDs, R/W DVDs, etc.

The instructions 122 are stored on memory 120 and executable by theprocessor(s) 118 to perform functions related to controlling the pulsercircuit 128 and the selector circuit 130, for generating 3D point clouddata, and for processing the 3D point cloud data (or perhapsfacilitating processing the 3D point cloud data by another computingdevice, such as the system controller 102).

The controller 116 can determine 3D point cloud data by using the lightemitters 124 to emit pulses of light. A time of emission is establishedfor each light emitter and a relative location at the time of emissionis also tracked. Aspects of an environment of the LIDAR device 110, suchas various objects, reflect the pulses of light. For example, when theLIDAR device 110 is in an environment that includes a road, such objectsmay include vehicles, signs, pedestrians, road surfaces, constructioncones, or the like. Some objects may be more reflective than others,such that an intensity of reflected light may indicate a type of objectthat reflects the light pulses. Further, surfaces of objects may be atdifferent positions relative to the LIDAR device 110, and thus take moreor less time to reflect portions of light pulses back to the LIDARdevice 110. Accordingly, the controller 116 may track a detection timeat which a reflected light pulse is detected by a light detector and arelative position of the light detector at the detection time. Bymeasuring time differences between emission times and detection times,the controller 116 can determine how far the light pulses travel priorto being received, and thus a relative distance of a correspondingobject. By tracking relative positions at the emission times anddetection times the controller 116 can determine an orientation of thelight pulse and reflected light pulse relative to the LIDAR device 110,and thus a relative orientation of the object. By tracking intensitiesof received light pulses, the controller 116 can determine howreflective the object is. The 3D point cloud data determined based onthis information may thus indicate relative positions of detectedreflected light pulses (e.g., within a coordinate system, such as aCartesian coordinate system) and intensities of each reflected lightpulse.

As described further below, the pulser circuit 128 is used for selectinglight emitters for emitting light pulses. The selector circuit 130similarly is used for sampling outputs from light detectors.

FIG. 2 illustrates an environment of a LIDAR device, according to anexample embodiment. In particular, FIG. 2 shows an environment 200 thatincludes a road 202, a LIDAR device (which is indicated schematically bya detection plane 204), and a plurality of objects. The LIDAR device maybe the same or similar to the LIDAR device 110. The detection plane 204is a simplified representation of the LIDAR device because, in practice,the LIDAR device may detect reflected portions of light pulses atmultiple heights and angles. The LIDAR device is positioned at a height208 relative to a road surface 206. In this context, the road 202 may beconsidered an object. The objects in the environment 200 further includeretroreflectors 210, 212, 214, and 216. The objects further include sign218, which includes a retroreflective strip 220.

The LIDAR device (or a controller thereof) may avoid emitting lighttowards retroreflective materials. For example, in a first scan at ornear to the detection plane 204, the LIDAR device may detect clusters ofhigh-intensity reflections (e.g., 95% or more of an emitted light pulseintensity). During a second scan, the LIDAR device may cause lightemitters to scan a first portion of the environment and not scan asecond portion. The second portion may include regions 222, 224, 226,228, and 230. By avoiding these areas, the LIDAR device reduces thelikelihood of receiving high-intensity reflections from these regions.The LIDAR device may determine positions and times of light emissionsthat would illuminate these regions based on orientations and distancesof received reflections relative to the detection plane 204. Withinother examples, a separate computing device (e.g., the system controller102) may perform these functions.

After determining which regions of the environment 200 to avoidilluminating, the LIDAR device selects light emitters for emittinglight, and selects light emitters for not emitting light. In exampleswhere only a single light emitter is used for emitting light (e.g.,where an adjustable mirror is used in conjunction with a single lightemitter to generate multiple light beams that are emitted into theenvironment) timing of the single light emitter or actions of acoordinating member (e.g., movement of an adjustable mirror) can beadjusted to emit light to some portions of an environment but notothers. Further description of this is provided below with respect toFIGS. 3A-3D.

FIG. 3A illustrates a pulser circuit of a LIDAR device at a first time,according to an example embodiment. In particular, FIG. 3A shows apulser circuit 300 that includes a voltage source node 302 that can beconnected to a voltage source (not depicted). For example, the voltagesource may be an adjustable voltage source. The voltage source node 302is connected to an inductor 304 at a first end. For example, theinductor may be a single inductor associated with the pulser circuit104. The inductor is connected to a first node 306 at a second end. Thepulser circuit 300 further includes a second node 308. A plurality ofcapacitors and corresponding light emitters (e.g., laser diodes) areconnected in parallel between the first node 306 and the second node 308through diodes 310, 318, 326, and 334, respectively.

Alternative portions of the environment 200 may be avoided by the LIDARdevice as well. These may be aspects of the environment detected by theLIDAR device or other sensors (e.g., the sensors 112). For example, aGPS device may indicate a location of the LIDAR device. The location ofthe LIDAR device may be associated with known static objects that arehighly reflective, and which may cause interference with reflectionsreceived from other objects in the environment. Based on thisinformation, the LIDAR device may avoid emitting light towards the knownstatic objects. In other examples where the LIDAR device is mounted to avehicle, the LIDAR device may avoid emitting light towards a detectedsurface of the vehicle (e.g., a hood or trunk of the vehicle). Otherexamples are possible. The example depicted in FIG. 2 is referencedbelow for illustrative purposes.

In FIG. 3A, four sets of capacitors and corresponding light emitters aredepicted. However, it should be understood that more or fewer sets canbe used. An anode end of a first diode 310 is connected to the firstnode 306 and a cathode end of the first diode 310 is connected to afirst common node. An anode end of a first light emitter 312 (depictedas a light-emitting diode) is connected to the first common node and acathode end of the first light emitter 312 is connected to the secondnode 308. A first end of a first capacitor 314 is connected to the firstcommon node and a second end of the first capacitor 314 is connected toground. The first common node is connected to a shift register 344. Theshift register 344 may include a plurality of discharge-controltransistors 350, 352, 354, and 356. In other examples, an output of theshift register 344 can be connected to gate of the discharge-controltransistors 350, 352, 354, and 356. Discharge-control transistor 350 isassociated with the first capacitor 314 at the first common node and isconfigured to selectively discharge the first capacitor 314 based on anoutput of the shift register 344.

Within examples, the shift register 344 may be loaded with N bits ofdata (e.g., corresponding to N capacitors and N corresponding lightemitters, or corresponding to as many as 2{circumflex over ( )}Ncapacitors and 2{circumflex over ( )}N corresponding light emittersdepending on how the shift register 344 is configured) using a digitalinput to the shift register, and each bit of data may control a state ofa discharge-control transistor. For example, a “1” may indicate that adischarge-control transistor is to be turned on and a “0” may indicatethat a discharge-control transistor is to remain off, or vice versa.Further, as noted above, discharge-control transistors 350, 352, 354,and 356 can be more generally referred to as “switches,” andcorrespondingly, other switching devices could be used and operatesimilarly to discharge-control transistors 350, 352, 354, and 356 asdescribed herein. Within examples, the discharge-control transistors arecontrolled directly by a LIDAR controller, such as controller 116. Otherimplementations are possible.

An anode end of a second diode 318 is connected to the first node 306and a cathode end of the second diode 318 is connected to a secondcommon node. An anode end of a second light emitter 320 (depicted as aphotodiode) is connected to the second common node and a cathode end ofthe second light emitter 320 is connected to the second node 308. Afirst end of a second capacitor 322 is connected to the second commonnode and a second end of the second capacitor 322 is connected toground. The second common node is connected to the shift register 344.The shift register 344 may include or be connected to adischarge-control transistor associated with the second capacitor 322 atthe second common node. In particular, discharge-control transistor 352is associated with the second capacitor 322 at the second common nodeand is configured to selectively discharge the second capacitor 322based on an output of shift register 344.

An anode end of a third diode 326 is connected to the first node 306 anda cathode end of the third diode 326 is connected to a third commonnode. An anode end of a third light emitter 328 (depicted as alight-emitting diode) is connected to the third common node and acathode end of the third light emitter 328 is connected to the secondnode 308. A first end of a third capacitor 330 is connected to the thirdcommon node and a second end of the third capacitor 330 is connected toground. The third common node is connected to a shift register 344. Theshift register 344 may include or be connected to a discharge-controltransistor associated with the third capacitor 330 at the third commonnode. In particular, discharge-control transistor 354 is associated withthe third capacitor 330 at the third common node and is configured toselectively discharge the third capacitor 330 based on an output ofshift register 344.

An anode end of a fourth diode 334 is connected to the first node 306and a cathode end of the fourth diode 334 is connected to a fourthcommon node. An anode end of a fourth light emitter 336 (depicted as alight-emitting diode) is connected to the fourth common node and acathode end of the fourth light emitter 336 is connected to the secondnode 308. A first end of a fourth capacitor 338 is connected to thefourth common node and a second end of the fourth capacitor 338 isconnected to ground. The fourth common node is connected to a shiftregister 344. The shift register 344 may include or be connected to adischarge-control transistor associated with the fourth capacitor 338 atthe fourth common node. In particular, discharge-control transistor 356is associated with the fourth capacitor 338 at the fourth common nodeand is configured to selectively discharge the fourth capacitor 338based on an output of shift register 344.

Within examples, cathode ends of the first light emitter 312, secondlight emitter 320, third light emitter 328, and fourth light emitter 336share a common cathode which forms the second node 308. For example, aunitary device (such as a chip or printed circuit board, may includeeach of the light emitters). The second node 308 is connected to apulse-control transistor 348 (depicted as a field effect transistor(FET), such as a MOSFET) at a drain end. The pulse-control transistor348 is connected to ground at a source end. A gate of the pulse-controltransistor 348 is controlled by a FET driver 346. The FET driver may beconfigured to operationally bias the pulse-control transistor 348 basedon control instructions such that the pulse-control transistor 348promotes current flow or restricts current flow (e.g., such that littleor no current flows from the second node 308 to ground). In otherexamples, an alternative to a transistor, such as a switch, can be used.

Also shown in FIG. 3A are a plurality of currents “I1” flowing throughthe respective diode and charging the respective capacitors or each set.This occurs at a first time at which the voltage source node 302provides a voltage input to the inductor 304, which in turn provides avoltage at the first node 306. The FET driver 346 controls thepulse-control transistor 348 so that it restricts current flow from thesecond node 308 to ground. Similarly, the discharge-control transistorsassociated with shift register 344 restrict current flow at the firsttime. In turn, this causes the current I1 (which may vary slightly basedon each diode and capacitor) to flow from the first node 306 to thecapacitors, causing the capacitors to charge.

Voltage indicators 316, 324, 332, and 340 are depicted in FIG. 3A forillustrative purposes, and correspond to capacitors 314, 322, 330, and338 respectively. The voltage indicators show a relative voltage level“Vcap” of each capacitors at different times. At the first time, eachcapacitor has zero or minimal charge because the input voltage node 302has just begun to provide a voltage.

FIG. 3B illustrates a pulser circuit of a LIDAR device at a second time,according to an example embodiment. In particular, FIG. 3B shows adifferent state of the pulser circuit 300 as shown in FIG. 3A anddescribed above. The second time might be the end of a first period thatspans the first time to the second time. The second time may alsocorrespond to the beginning of a second period. The first period and thesecond period may be portions of a repeating pulse period of the pulsercircuit 300.

At the second time, each capacitor has been charged, as shown by voltageindicators 316, 324, 332, and 340. Though these indicate a maximum Vcaphas been reached, depending on a voltage level at the first node 306 anda time taken to charge the capacitors, a different voltage may bereached. For example, in a default mode of operation, an adjustablevoltage source connected to the voltage source node 302 may becontrolled to apply a voltage V1 to the inductor 304, which causes eachof the capacitors to charge up to a voltage of Vcap1 (e.g., Vcap1 couldbe about 2×V1). When the capacitors discharge through their respectivelaser diodes, as described further below, the emitted light pulses mayhave a first peak power level. However, for relatively short periods oftime (e.g., based on thermal constraints), the adjustable voltage sourcemay be controlled to apply a voltage V2 to the inductor in which V2>V1.This causes the capacitors to charge up to a higher voltage, Vcap2(e.g., Vcap2 could be about 2×V2). Thus, when the capacitors dischargethrough their respective laser diodes, the emitted light pulses may havea second, higher peak power level. In this manner, the pulser circuit300 can be controlled to emit light from the light emitters at differentintensities, which can allow for more nuanced control of the LIDARdevice. For example, increased light intensities may be used where theenvironment is relatively bright (e.g., based on other light sources inthe environment), while lower light intensities can be used in low-lightconditions (e.g., at night) to conserve energy usage.

In additional or alternative examples, controlling the voltage levels ofthe capacitors may alternatively or additionally involve applying avoltage for a period of time associated with charging the capacitor. Forexample, a desired power level of a light pulse can be determined thatis associated with a charge level of the capacitors. The capacitors maybe charged for a period of time (e.g., based on a known capacitance ofthe capacitors and the applied voltage) associated with the power level.Because the capacitance of each capacitor is predetermined and a voltageoutput at the first node 306 is known (e.g., controlled to be at aparticular voltage level), charging characteristics of each capacitorcan be used to accurately set the charge level of the capacitors. Forexample, a time constant can be determined and used to calculate acharging time for the capacitors. In this manner, a power level of eachlight pulse can be precisely controlled by setting the charging periodfor the capacitors. Additionally or alternatively, each chargedcapacitor can be discharged by a predetermined amount prior to theemission period to achieve a desired voltage level and thereby control apower level of each light pulse.

Turning back to FIG. 3B, a plurality of currents “I2” are shown thatcorrespond to capacitors 314 and 330. This is caused usingdischarge-control transistors 350 and 354 corresponding to capacitors314 and 330, as shown in shift register 344 of FIG. 3B. As noted above,in other implementations, these transistors may exist separately fromthe shift register 344 and operate based on outputs of the shiftregister. Thus, at the second time, all of the capacitors are chargedand capacitors 314 and 330 have been selected for discharging. Further,because the FET driver 346 controls the pulse-control transistor 348 sothat it restricts current flow from the second node 308 to ground, zeroor minimal current flows through the light emitters at the second time.

Discharging capacitors 314 and 330 corresponds to not emitting light (oremitting a relatively low level of light) from light emitters 312 and328 respectively. Using FIG. 2 as a reference scenario for illustrativepurposes, based on a status of a LIDAR device that includes the lightemitters (e.g., a location of the LIDAR device), and based on regions ofthe environment that the LIDAR device is avoiding (e.g., regions 228 and230 corresponding to retroreflector 216 and retroreflective strip 220),some light detectors might be “turned off” for a given pulse period toavoid emitting light towards the regions of the environment that theLIDAR device is avoiding. For example, the LIDAR device (or anotherdevice, such as the system controller 102) may determine which lightemitters are scheduled to emit light towards the avoided regions, andselect corresponding capacitors for discharging so that those lightemitters do not emit light. In the present example, this includesdischarging capacitors 314 and 330 so that light emitters 312 and 328 donot emit light so that the LIDAR device does not illuminate regions 228and 230. As referred to below with respect to FIG. 4, this process mayinvolve determining a portion of an environment to illuminate using thelight emitters and a remaining portion. The remaining portion maycorrespond to regions that the LIDAR device avoids illuminating with oneor more light emitters.

FIG. 3C illustrates a pulser circuit of a LIDAR device at a third time,according to an example embodiment. In particular, FIG. 3C shows adifferent state of the pulser circuit 300 as shown in FIGS. 3A and 3Band described above. The third time might be the end of a second periodthat spans the second time to the third time. The third time may alsocorrespond to the beginning of a third period. The second period and thethird period may be portions of a repeating pulse period of the pulsercircuit 300.

As shown by voltage indicators 316 and 332 corresponding to capacitors314 and 330 respectively have zero or minimal voltage as a result ofbeing discharged during the second period. Also shown are a plurality ofcurrents “I3” from capacitors 322 and 338 to the second node 308 andcurrent “I4” from the second node to ground. At the third time, the FETdriver 346 controls the pulse-control transistor 348 so that it promotescurrent flow from the second node 308 to ground, the currents I3 and I4are permitted to flow across light emitters 312 and 336 fromcorresponding capacitors 322 and 338, thereby causing light emitters 312and 336 to emit light. Returning again to FIG. 2 for illustrativepurposes, light emitters 312 and 336 may be directed to portions of theenvironment other than regions 222, 224, 226, 228, and 230, and thuscorrespond to the portion of the environment illuminated using the lightemitters.

FIG. 3D illustrates a pulser circuit of a LIDAR device at a fourth time,according to an example embodiment. In particular, FIG. 3D shows adifferent state of the pulser circuit 300 as shown in FIGS. 3A, 3B, and3C and described above. The fourth time might be the end of a thirdperiod that spans the third time to the fourth time. The third periodmay be a portion of a repeating pulse period of the pulser circuit 300.In other examples, a latent period may extend from the fourth time to abeginning time of another pulse period, depending on scanningfrequencies of the LIDAR device. As shown in voltage indicators 316,324, 332, and 338, after the third time, each of the capacitors isdischarged and the pulser circuit 300 can begin another pulse periodduring which different light emitters might be selection for emittinglight or not emitting light depending on a status of the LIDAR deviceand/or the surrounding environment.

III. Example Methods

FIG. 4 is a block diagram of a method, according to an exampleembodiment. In particular, FIG. 4 depicts a method 400 for use inselectively emitting light from a plurality of light emitters. Method400 may be implemented in accordance with system 100, the pulser circuit300 or the description thereof. For example, aspects of the functions ofmethod 400 may be performed by system controller 102, controller 116, orby logical circuitry configured to implement the functions describedabove with respect to FIGS. 1A, 1B, 2, 3A, 3B, 3C, and 3D.

At block 402, method 400 includes, during a first period (e.g., betweenthe first time and the second time shown in FIGS. 3A and 3Brespectively), (i) using a pulse-control switch to restrict current flowthrough a plurality of light emitters, and (ii) charging a plurality ofcapacitors via a first node. This may be performed in accordance withFIGS. 3A, 3B, and corresponding description thereof.

At block 404, method 400 includes, during a second period (e.g., betweenthe second time and the third time shown in FIGS. 3B and 3Crespectively), using one or more discharge-control switches to allowcurrent flow that discharges one or more corresponding capacitors of theplurality of capacitors. This may be performed in accordance with FIGS.3B, 3C, and corresponding description thereof.

At block 406, method 400 includes, during a third period (e.g., betweenthe third time and the fourth time shown in FIGS. 3C and 3Drespectively), using the pulse-control switch to allow current flow andthereby discharge one or more undischarged capacitors of the pluralityof capacitors through one or more corresponding light emitters of theplurality of light emitters, thereby causing the one or morecorresponding light emitters to emit respective pulses of light. Thismay be performed in accordance with FIGS. 3B, 3C, and correspondingdescription thereof.

Within examples, method 400 further includes determining a portion of anenvironment to illuminate using the light emitters and a remainingportion. For example, in a default state of a LIDAR device, this mayinclude an entire field of view associated with a range of motion oflight emitters in the LIDAR device. In other states, such as thatdepicted in FIG. 2, this may involve a majority of the environment minussome regions that the LIDAR device avoids. In these examples, method 400includes determining one or more light emitters corresponding to theremaining portion of the environment at an emission time (e.g., lightemitters 312 and 332). In such examples block 404 involves using the oneor more discharge-control switches to allow current flow and therebydischarge the one or more light emitters corresponding to the remainingportion of the environment. In this manner, method 400 allowsilluminating select portions of the environment. As an example of theseembodiments, determining the portion of an environment to illuminateusing the light emitters and the remaining portion includes emittinglight using the light emitters during a first scan of the environment(e.g., as described above with respect to FIG. 2), receiving reflectedportions of the emitted light corresponding to the first scan, anddetermining, based on the received reflected portions of emitted light,not to emit light towards the remaining portion of the environmentduring a second scan of the environment. For example, this maycorrespond to not emitting light towards regions 222, 224, 226, 228, and230 depicted in FIG. 2. In still further examples, method 400 mayinclude identifying, based on the received reflected portions of emittedlight, a type of object in the environment (e.g., a retroreflector). Insuch examples determining not to emit light towards the remainingportion of the environment during the second scan of the environmentincludes determining not to emit light towards the type of object in theenvironment. For example, the region may be determined based onidentifying a portion of a field of view of the LIDAR devicecorresponding to the retroreflectors in the first scan, determining abuffer region (e.g., 6 inches) around the identified retroreflectors,and not emitting light within portion of the fields of view and/or thebuffer region.

Within examples in which the one or more discharge-control switchescorrespond to outputs from a shift register, block 404 may include usingthe one or more discharge-control switches to allow current flow andthereby discharge one or more of the plurality of capacitors, comprisesusing a plurality of bits input into the shift register to designatewhich of the plurality of capacitors is discharged during the secondperiod and which of the plurality of capacitors are undischarged duringthe second period.

Within examples in which the method is implemented using a LIDAR device(e.g., the LIDAR device 110), method 400 can further include determiningan expected change in pose of the LIDAR device from a first scan of theLIDAR device to a second scan of the LIDAR device. For example, if theLIDAR is coupled to a vehicle, a controller of the vehicle (e.g., systemcontroller 102) may determine a velocity of the vehicle and determinewhere the LIDAR device will be during the second scan. In such examples,block 404 further includes selecting the one or more of the plurality ofcapacitors for discharging based on the expected change in pose of theLIDAR device from the first scan of the LIDAR device to the second scanof the LIDAR device. For example, the expected pose may influence whichlight emitter is scheduled to illuminate a region that the LIDAR deviceshould avoid illuminating.

Within examples, method 400 may be performed multiple times insuccession, with different light emitters being selected for emittinglight and not emitting light in different iterations. In this manner thesystems and methods described herein may adapt to changing conditions inthe environment or different instructions received, for example, fromthe system controller 102. For example, the first period, the secondperiod, and the third period are included within a first pulse period ofa plurality of repeating pulse periods associated with the plurality oflight emitters. And, during a second pulse period of the plurality ofpulse periods the first, second, and third periods may be performedagain using different light emitters. Namely, during the first period ofthe second pulse period, method 400 includes (i) using the pulse-controlswitch to restrict current flow through a plurality of light emitters,and (ii) charging the plurality of capacitors via a first node. Further,during the second period of the second pulse period, method 400 includesusing the one or more discharge-control switches to allow current flowand thereby discharge one or more different capacitors of the pluralityof capacitors. Additionally, during the third period of the second pulseperiod, method 400 includes using the pulse-control switch to allowcurrent flow and thereby discharge one or more different undischargedcapacitors through one or more different light emitters causing the oneor more different light emitters to emit respective pulses of light.

Though particular embodiments described herein show certain ways ofcharging and discharging capacitors within pulse periods as a way ofselecting particular light emitters for emitting light or not emittinglight, different ways of achieving this are possible. For example,different types of transistors or diodes can be used, or switches orother devices capable of imposing discrete states on a pulser circuitcan be used in various implementations and within the contemplated scopeof this disclosure. Further, though operations described herein refer tocomputing devices such as system controller 102, and controller 116, itshould be understood that the functions described herein may beperformed by either of these computing devices, both computing devices,or neither computing device. For example, logical circuitry and periodictiming circuits can be used to perform aspects of this disclosure bydefault or automatically. Further, though embodiments are described witha certain number of light emitters, it should be understood thatsubstantially more light emitters (or, in other examples, fewer lightemitters, such as one light emitter) may be included in a single pulsercircuit depending on contexts of the system (e.g., some LIDAR devicescan include a single light emitter, while others may include several).In other examples, several pulser circuits may run concurrently to driveall light emitters in a LIDAR device. Other examples are possible.

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anillustrative embodiment may include elements that are not illustrated inthe Figures.

A step or block that represents a processing of information cancorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information can correspond to a module, a segment, aphysical computer (e.g., a field programmable gate array (FPGA) orapplication-specific integrated circuit (ASIC)), or a portion of programcode (including related data). The program code can include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data can be stored on any type of computer readable medium suchas a storage device including a disk, hard drive, or other storagemedium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that store data for shortperiods of time like register memory, processor cache, and random accessmemory (RAM). The computer readable media can also includenon-transitory computer readable media that store program code and/ordata for longer periods of time. Thus, the computer readable media mayinclude secondary or persistent long term storage, like read only memory(ROM), optical or magnetic disks, compact-disc read only memory(CD-ROM), for example. The computer readable media can also be any othervolatile or non-volatile storage systems. A computer readable medium canbe considered a computer readable storage medium, for example, or atangible storage device.

While various examples and embodiments have been disclosed, otherexamples and embodiments will be apparent to those skilled in the art.The various disclosed examples and embodiments are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

What is claimed is:
 1. A circuit comprising: a plurality of lightemitters connected between a first node and a second node; a pluralityof capacitors, wherein each capacitor in the plurality of capacitorscorresponds to a respective light emitter in the plurality of lightemitters; a plurality of discharge-control switches, wherein eachdischarge-control switch corresponds to a respective capacitor in theplurality of capacitors; and a pulse-control switch connected to theplurality of light emitters, wherein, during a first period, thepulse-control switch restricts current flow and each capacitor in theplurality of capacitors is charged via the first node, wherein, during asecond period, one or more of the plurality of discharge-controlswitches allows current flow that discharges one or more correspondingcapacitors of the plurality of capacitors, and wherein, during a thirdperiod, the pulse-control switch allows current flow that discharges oneor more undischarged capacitors of the plurality of capacitors throughone or more corresponding light emitters of the plurality of lightemitters, thereby causing the one or more corresponding light emittersto emit respective pulses of light.
 2. The circuit of claim 1, whereinthe pulse-control switch comprises a field-effect transistor.
 3. Thecircuit of claim 1, wherein the plurality of light emitters comprises aplurality of laser diodes sharing a common cathode, and wherein thecommon cathode is connected to the pulse-control switch at the secondnode.
 4. The circuit of claim 1, further comprising a shift registerconfigured to select individual capacitors from the plurality ofcapacitors, via corresponding discharge-control switches in theplurality of discharge-control switches, for discharging.
 5. The circuitof claim 4, wherein the shift register is configured to receive adigital input comprising a plurality of bits, wherein each bit in theplurality of bits indicates whether a corresponding capacitor in theplurality of capacitors is discharged or undischarged during the secondperiod.
 6. The circuit of claim 1, further comprising a plurality ofdiodes connected between the first node and the plurality of capacitors,wherein each capacitor of the plurality of capacitors is charged via acorresponding diode of the plurality of diodes.
 7. The circuit of claim1, further comprising a driver circuit connected to the pulse-controlswitch and configured to bias the pulse-control switch to allow currentflow during the third period.
 8. The circuit of claim 1, wherein thefirst period, the second period, and the third period, occur within arepeating pulse period associated with the plurality of light emitters.9. The circuit of claim 1, further comprising a single inductorconnected to the first node, wherein the single inductor is configuredto charge the plurality of capacitors during the first period.
 10. Thecircuit of claim 1, further comprising an adjustable voltage sourceconnected to the first node, wherein the plurality of capacitors arecharged during the first period in accordance with a voltage level ofthe adjustable voltage source, and wherein the respective pulses oflight emitted during the third period have a peak power level that isbased on the voltage level.
 11. A method comprising: during a firstperiod, (i) using a pulse-control switch to restrict current flowthrough a plurality of light emitters, and (ii) charging a plurality ofcapacitors via a first node; during a second period, using one or moredischarge-control switches to allow current flow that discharges one ormore corresponding capacitors of the plurality of capacitors; and duringa third period, using the pulse-control switch to allow current flow andthereby discharge one or more undischarged capacitors of the pluralityof capacitors through one or more corresponding light emitters of theplurality of light emitters, thereby causing the one or morecorresponding light emitters to emit respective pulses of light.
 12. Themethod of claim 11, further comprising: determining a portion of anenvironment to illuminate using the light emitters and a remainingportion; and determining one or more light emitters corresponding to theremaining portion of the environment at an emission time, wherein usingthe one or more discharge-control switches to allow current flow andthereby discharge the one or more of the plurality of capacitorscomprises using the one or more discharge-control switches to allowcurrent flow and thereby discharge the one or more light emitterscorresponding to the remaining portion of the environment.
 13. Themethod of claim 12, wherein determining the portion of an environment toilluminate using the light emitters and the remaining portion comprises:emitting light using the light emitters during a first scan of theenvironment; receiving reflected portions of the emitted lightcorresponding to the first scan; determining, based on the receivedreflected portions of emitted light, not to emit light towards theremaining portion of the environment during a second scan of theenvironment.
 14. The method of claim 13, further comprising:identifying, based on the received reflected portions of emitted light,a type of object in the environment, wherein determining not to emitlight towards the remaining portion of the environment during a secondscan of the environment comprises determining not to emit light towardsthe type of object in the environment.
 15. The method of claim 14,wherein the type of object is a retroreflector.
 16. The method of claim11, wherein the one or more discharge-control switches correspond tooutputs from a shift register, and wherein using the one or moredischarge-control switches to allow current flow and thereby dischargeone or more of the plurality of capacitors, comprises using a pluralityof bits input into the shift register to designate which of theplurality of capacitors is discharged during the second period and whichof the plurality of capacitors are undischarged during the secondperiod.
 17. The method of claim 11, wherein the method is implementedusing a LIDAR device, the method further comprising: determining anexpected change in pose of the LIDAR device from a first scan of theLIDAR device to a second scan of the LIDAR device, wherein using the oneor more discharge-control switches to allow current flow and therebydischarge one or more of the plurality of capacitors, comprises:selecting the one or more of the plurality of capacitors for dischargingbased on the expected change in pose of the LIDAR device from the firstscan of the LIDAR device to the second scan of the LIDAR device.
 18. Themethod of claim 11, wherein the first period, the second period, and thethird period are comprised within a first pulse period of a plurality ofrepeating pulse periods associated with the plurality of light emitters,the method further comprising: during a second pulse period of theplurality of pulse periods; during the first period of the second pulseperiod, (i) using the pulse-control switch to restrict current flowthrough a plurality of light emitters, and (ii) charging the pluralityof capacitors via a first node; during the second period of the secondpulse period, using the one or more discharge-control switches to allowcurrent flow that discharges one or more different capacitors of theplurality of capacitors; and during the third period of the second pulseperiod, using the pulse-control switch to allow current flow and therebydischarge one or more different undischarged capacitors through one ormore different light emitters, thereby causing the one or more differentlight emitters to emit respective pulses of light.
 19. A non-transitorycomputer readable medium having instructions stored thereon that whenexecuted by a processor cause performance of a set of functions, whereinthe set of functions comprises: during a first period, (i) using apulse-control switch to restrict current flow through a plurality oflight emitters, and (ii) charging a plurality of capacitors via a firstnode; during a second period, using one or more discharge-controlswitches to allow current flow that discharges one or more correspondingcapacitors of the plurality of capacitors; and during a third period,using the pulse-control switch to allow current flow and therebydischarge one or more undischarged capacitors of the plurality ofcapacitors through one or more corresponding light emitters of theplurality of light emitters, thereby causing the one or morecorresponding light emitters to emit respective pulses of light.
 20. Thenon-transitory computer readable medium of claim 19, wherein the set offunctions further comprise: emitting light using the light emittersduring a first scan of an environment; receiving reflected portions ofthe emitted light corresponding to the first scan; determining, based onthe received reflected portions of emitted light, a portion of anenvironment to illuminate using the light emitters and a remainingportion; and determining one or more light emitters corresponding to theremaining portion of the environment at an emission time, wherein usingthe one or more discharge-control switches to allow current flow andthereby discharge the one or more of the plurality of capacitorscomprises using the one or more discharge-control switches to allowcurrent flow that discharges the one or more light emitterscorresponding to the remaining portion of the environment.